The present invention relates to image pickup devices, and more particularly to a highly sensitive and high resolution image pickup device capable of picking up images without generating distortions around the peripheral parts of the picture screen. A voltage of a predetermined correction waveform is applied to a grid of the image pickup tube of the image pickup device.
Generally, as compared to a magnetic focus type image pickup tube, in an electrostatic focus type image pickup tube, a focus coil on a deflection yoke can be eliminated, and the miniaturization of the image pickup camera is facilitated, hence often being used nowadays. However, especially when the above type is used in a color television camera, high sensitivity and high resolution is required of the image pickup device.
In order to obtain normalized and high resolution of the image pickup tube throughout a whole target surface, the voltage ratio which forms the collimation of the image pickup tube must be set to a value higher than a certain value.
However, as will be described in the following in conjunction with the drawings, when the above voltage ratio is set to a high value, the equipotential line of the collimation electronic lens curves by a large amount, and thus the electron beam which passes through this collimation electronic lens is bent by a large amount. Accordingly, the area of the effective scanning surface on the target surface which is scanned by the electron beam becomes small.
On the other hand, in order to set the sensitivity of the image pickup tube to a high value, the area of the effective scanning surface of the targert surface which is traced by the electron beam must be large.
When the collimation voltage ratio is set to a value larger than a predetermined value in order to otain both high resolution and high sensitivity in the image pickup tube, and when the incidence range of the electron beam entering the collimation electron lens as incident light is set to a large value in order to set the area of the effective scanning surface to a large value, the electron beam hits the inner wall of the grid used for the formation of the collimation electronic lens. Therefore, when the video signal obtained by the image pickup performed by use of the image pickup tube in the above state is reproduced on the picture screen of the receiver, distortion is introduced at the peripheral parts of the picture screen, especially at the four corners of the picture screen.